With technical improvement in recent years, liquid crystal displays (LCDs), plasma display panels (PDPs), electroluminescence displays (ELDs), etc. have been developed in addition to conventional cathode ray tubes (CRTs) as image displays and have been used practically. As LCDs have been technically improved to provide wide viewing angles, high resolution, high response, good color reproduction, and the like, applications of LCDs are spreading from laptop personal computers and monitors to television sets. In a basic LCD structure, a pair of flat glass substrates each provided with a transparent electrode are opposed via a spacer to form a constant gap, between which a liquid crystal material is placed and sealed to form a liquid crystal cell, and a polarizing plate is formed on the outside surface of each of the pair of glass substrates. In a conventional technique, a glass or plastic cover plate is attached to the surface of the liquid crystal cell in order to prevent scratches on the polarizing plate bonded to the surface of the liquid crystal cell. However, the placement of such a cover plate is disadvantageous in terms of cost and weight. Thus, a hard coating process has gradually been used to treat the surface of polarizing plates. It is common in the hard-coating process that a hard-coated antiglare film is used so as to serve also to prevent, for example, reflection of a light source onto LCDs.
A hard-coated antiglare film is used in which a thin hard-coating layer with a thickness of 2 to 10 μm has been formed on one or both surface of a transparent plastic film substrate. The hard-coating layer is formed using resins for forming a hard-coating layer such as thermosetting resins or ultraviolet(UV)-curable resins and fine particles. The surface of the hard-coating layer is provided with unevenness by the fine particles so as to provide antiglare properties. If such resins are applied to a glass plate to form the hard-coating layer, it can exhibit a pencil hardness of 4 H or more. If a hard-coating layer with an insufficient thickness is formed on a transparent plastic film substrate, however, the pencil hardness of the layer can be generally affected by the substrate and reduced to 3 H or less.
LCD applications have come to include home television sets, and thus it is easily expected that the users of general home television sets should handle LCD television sets in the same manner as in the case of conventional glass CRT television sets. Glass CRTs have a pencil hardness of about 9 H. Thus, hard-coated antiglare films to be used for LCDs have been required to have higher hardness.
An increase in the hardness of hard-coated antiglare films is possible by increasing the thickness of their hard-coating layer. However, the increase in layer thickness can cause a problem in that the particles are completely buried in the hard-coating layer and cannot provide sufficient antiglare properties. The addition amount of the fine particles may be increased to improve the antiglare properties, but in such a method, the number of the particles is increased in the layering direction, which causes a problem of high haze value. Recently, therefore, methods for overcoming the drawbacks of trying to achieve high hardness of hard-coated films, such as antiglare properties and increase in haze value, have been proposed, as disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 11-286083, 2000-326447, 2001-194504, and 2001-264508.
JP-A No. 11-286083 discloses a hard-coated antiglare film comprising a transparent substrate film and a hard-coating layer that is formed on the transparent substrate film and mainly composed of particles with an average particle size of 0.6 to 20 μm, fine particles with an average particle size of 1 to 500 nm and a hard-coating resin. It also discloses that the thickness of the hard-coating layer is at most the particle size of the particles, preferably at most 80% of the average particle size (specifically at most 16 μm).
JP-A No. 2000-326447 discloses a hard-coated film comprising a plastic substrate film and at least one hard-coating layer formed on at least one surface of the plastic substrate film, wherein the hard-coating layer has a thickness of 3 to 30 μm, and the hard-coating layer contains inorganic fine particles with secondary particle sizes of at most 20 μm. It also discloses that the surface of the hard-coating layer is provided with unevenness so as to provide antiglare properties.
JP-A No. 2001-194504 discloses an antireflection film comprising a plastic film and a laminate that is formed on at least one surface of the plastic film and comprises a hard-coating layer and thin antireflection film layer mainly composed of a metal alkoxide and a hydrolysate thereof, wherein the hard-coating layer has an elastic modulus of 0.7 to 5.5 GPa or lower at its breaking strain. It also discloses that the hard-coating layer has a thickness of 0.5 to 20 μm and that the hard-coating layer contains fine particles with an average particle size of 0.01 to 10 μm.
JP-A No. 2001-264508 discloses an antiglare antireflection film comprising a transparent support and a laminate that is formed on the transparent support and sequentially comprises an antiglare hard-coating layer containing particles with an average particle size of 1 to 10 μm and a low-refractive-index layer with a refractive index of 1.35 to 1.49 produced with a composition containing inorganic fine particles with an average particle size of 0.001 to 0.2 μm, a hydrolysate of a photo-curable organosilane and/or a partial condensate thereof, and a fluoropolymer, wherein the antiglare antireflection film has a haze value of 3 to 20% and an average reflectance of at most 1.8% at wavelengths of 450 nm to 650 nm. It also discloses that the antiglare hard-coating layer has a thickness of 1 to 10 μm.
However, in such conventional hard-coated antiglare films, problems in both hardness and antiglare properties have not been solved satisfactorily. In JP-A No. 11-286083, there is a problem in that when the hard-coating layer has a thickness approximately in the above-mentioned range, a sufficiently high hardness cannot be obtained. In JP-A No. 2000-326447, there is the following problem. That is, in such a structure as described above, no consideration is given to the surface roughness of the hard-coating layer surface, and when the structure allows the inorganic fine particles to be buried completely in the hard-coating layer, sufficiently high antiglare properties cannot be obtained. Although the antireflection film as described in JP-A No. 2001-194504 has improved hardness and scratch resistance, there is a problem in that for example, when fine particles with an average particle size of about 1.8 sum are added to a hard-coating layer with a thickness of about 20 Elm, fine particles are buried completely in the hard-coating layer and cannot provide sufficiently high antiglare properties. The antiglare antireflection film as described in JP-A No. 2001-264508 is intended to improve the scratch resistance, antiglare properties, etc., but there is a problem in that a sufficiently high hardness is not obtained.